In a typical cooling system for a four-stroke V-type marine engine, cooling water is drawn from the engine block by a circulating pump and passes through a thermostat housing and is returned to the block, while fresh sea water is drawn to the thermostat housing by a sea water pick-up pump. When the thermostat is closed, the incoming sea water is mixed with the circulating cooling water in the thermostat housing and a portion of the mixed water is discharged through the exhaust elbows to overboard. When the thermostat valve is opened, a portion of the circulating water returned from the block is discharged through the exhaust manifolds to overboard.
With a cooling system of this type, the thermostat housing contains numerous ports or openings and internal chambers. For example, the housing is provided with a pair of inlet openings, one to receive water returned from the block, while the other receives incoming fresh sea water. In addition, the housing has an outlet communicating with the block circulating pump, a pair of outlets which communicate with the exhaust manifolds, and a second pair of outlets which are connected to the exhaust elbows. Further, the typical thermostat housing has a pair of holes for the pressure and temperature transducers. In the past, the thermostat housing has been sand cast from a ferrous metal and, due to the complexity of the housing configuration, the casting has been extremely complicated and expensive, requiring the use of extensive coring.
Evaporable foam casting procedures have been used for casting metal components of internal combustion engines, such as marine engines. In the typical evaporable foam process, a pattern is produced having a configuration identical to the metal part to be cast. The foam pattern is placed in a mold and a finely divided, unbonded material, such as sand, is placed around the pattern in the mold, and also fills the cavities in the mold. During casting, the molten metal will contact the evaporable foam pattern, causing the pattern to vaporize with the vapor being entrapped within the interstices of the sand, while the molten metal fills the void created by vaporization of the foam, thus resulting in a cast metal part which has a configuration identical to that of the foam pattern.
In some instances, evaporable foam casting enables a part to be cast as a single integral piece, thus eliminating the labor and material costs of connecting multiple cast parts to provide the final product.
In other situations, evaporable foam casting enables a part to be cast without the use of a complicated and expensive internal coring, and thus reduces the overall cost of the casting process.